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Research Papers: Design and Analysis

The Beneficial Contribution of Realistic Autofrettage to the Load-Carrying Capacity of Thick-Walled Spherical Pressure Vessels

[+] Author and Article Information
M. Perl1

Departamento de Ingenierıá Mecánica y Metalúrgica, Pontificia Universidad Católica de Chile, Avda. Vicunã Mackenna 4860, Santiago de Chile, Chile

J. Perry

Department of Mechanical Engineering, Pearlstone Center for Aeronautical Engineering Studies, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel

1

On a sabbatical leave from the Department of Mechanical Engineering, Pearlstone Center for Aeronautical Engineering Studies, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.

J. Pressure Vessel Technol 132(1), 011204 (Jan 04, 2010) (6 pages) doi:10.1115/1.4000513 History: Received July 22, 2009; Revised September 23, 2009; Published January 04, 2010; Online January 04, 2010

Increased strength-to-weight ratio and extended fatigue life are the main objectives in the optimal design of modern pressure vessels. These two goals can mutually be achieved by creating a proper residual stress field in the vessel’s wall by a process known as autofrettage. Although there are many studies that have investigated the autofrettage problem for cylindrical vessels, only a few of such studies exist for spherical ones. Because of the spherosymmetry of the problem, autofrettage in a spherical pressure vessel is treated as a one-dimensional problem and solved solely in terms of the radial displacement. The mathematical model is based on the idea of solving the elastoplastic autofrettage problem using the form of the elastic solution. Substituting Hooke’s equations into the equilibrium equation and using the strain-displacement relations yield a differential equation, which is a function of the plastic strains. The plastic strains are determined using the Prandtl–Reuss flow rule and the differential equation is solved by the explicit finite difference method. The existing 2D computer program, for the evaluation of hydrostatic autofrettage in a thick-walled cylinder, is adapted to handle the problem of spherical autofrettage. The presently obtained residual stress field is then validated against three existing solutions emphasizing the major role the material law plays in determining the autofrettage residual stress field. The new code is applied to a series of spherical pressure vessels yielding two major conclusions. First, the process of autofrettage increases considerably the maximum safe pressure that can be applied to the vessel. This beneficial effect can also be used to reduce the vessel’s weight rather than to increase the allowable internal pressure. Second, the specific maximum safe pressure increases as the vessel becomes thinner. The present results clearly indicate that autofrettaging of spherical pressure vessels can be very advantageous in various applications.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

High blast containment vessel

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Figure 2

Material behavior during the autofrettage process

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Figure 3

The universal tensile stress-strain curve

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Figure 4

Yield stress Bauschinger effect factor in compression

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Figure 5

The universal compressive stress-strain curve

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Figure 6

Yield stress Bauschinger effect factor in tension

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Figure 7

Comparison between the present and the analytical solutions

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Figure 8

Comparison between the present and the ROKH solutions

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Figure 9

Comparison between the present and the VMPs solutions

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Figure 10

Residual stress distribution for an autofrettaged spherical vessel η=1.25

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Figure 11

The SMP stress distribution for autofrettaged and nonautofrettaged spherical vessels

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Figure 12

The SMP and weight values as a function of the radii-ratio

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